Power consumption by electronic devices is an increasingly important factor in the design of electronic devices. From a global perspective, the energy consumption of electronic devices occupies a sizable percentage of total energy usage due to large corporate data centers and the ubiquity of personal computing devices. Environmental concerns thus motivate efforts to reduce the power consumed by electronic devices to help conserve the earth's resources. From an individual perspective, less power consumption translates to lower energy bills. Furthermore, many personal computing devices are portable and powered by batteries. The less energy that is consumed by a portable battery-powered electronic device, the longer the portable device may operate without recharging the battery. Lower energy consumption also enables the use of smaller batteries and the adoption of thinner form factors, which means electronic devices can be made more portable or versatile. Thus, the popularity of portable devices also motivates efforts to reduce the power consumption of electronic devices.
An electronic device consumes power if the device is coupled to a power source and is turned on. This is true for the entire electronic device, but it is also true for individual parts of the electronic device. Hence, power consumption can be reduced if parts of an electronic device are powered down, even while other parts remain powered up. Entire discrete components of an electronic device, such as a whole integrated circuit (IC) or a Wi-Fi radio, may be powered down. Alternatively, selected parts of a discrete component may likewise be powered down. For example, a distinct processing entity or other circuit block of an integrated circuit chip, such as a core thereof, may be selectively powered down for some period of time to reduce energy consumption.
A portion of an integrated circuit, such as a core, can therefore be powered down to reduce power usage and extend battery life. A core can be powered down by decoupling the core from a power source or by turning the power source off. Additionally, a core can be powered down by lowering a voltage supplied to the core to reduce power consumption. Powering down an integrated circuit portion is referred to herein as a “power collapse,” a “power collapse event,” or as creating a “power collapse period.”
Unfortunately, implementing a power collapse with an integrated circuit core can create problems. For example, resuming a computing task after a core is powered down takes time, which slows performance and can adversely impact a user experience. Moreover, functional data, which includes data being used for an ongoing computing task, may be lost if power is removed from certain types of computer memory. Losing functional data forces an application to restart or can even permanently damage user files, such as documents or pictures. Consequently, conserving energy using power collapse events is made more difficult because of the risks to functional data that arise from powering down a core of an integrated circuit.